Method of depositing a diffusion barrier for copper interconnect applications

ABSTRACT

The present invention pertains to methods for forming a metal diffusion barrier on an integrated circuit wherein the formation includes at least two operations. The first operation deposits barrier material via PVD or CVD to provide some minimal coverage. The second operation deposits an additional barrier material and simultaneously etches a portion of the barrier material deposited in the first operation. The result of the operations is a metal diffusion barrier formed in part by net etching in certain areas, in particular the bottom of vias, and a net deposition in other areas, in particular the side walls of vias. Controlled etching is used to selectively remove barrier material from the bottom of vias, either completely or partially, thus reducing the resistance of subsequently formed metal interconnects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.13/904,464 filed May 29, 2013, titled “Method of Depositing a DiffusionBarrier for Copper Interconnect Applications” by Rozbicki et al., whichis a continuation of U.S. patent application Ser. No. 12/764,870 filedApr. 21, 2010 (now abandoned), titled “Method of Depositing a DiffusionBarrier for Copper Interconnect Applications” by Rozbicki et al., whichis a continuation of U.S. patent application Ser. No. 11/714,465 filedMar. 5, 2007 (now U.S. Pat. No. 7,732,314), titled “Method forDepositing a Diffusion Barrier for Copper Interconnect Applications” byDanek et al., which is a continuation of U.S. patent application Ser.No. 10/804,353 filed Mar. 18, 2004 (now U.S. Pat. No. 7,186,648), titled“Barrier First Method For Single Damascene Trench Applications,” namingRozbicki et al. as inventors, which is a continuation-in-part of U.S.patent application Ser. No. 10/412,562 filed Apr. 11, 2003 (now U.S.Pat. No. 6,764,940), which is a continuation-in-part of U.S. patentapplication Ser. No. 09/965,472 filed Sep. 26, 2001 (now U.S. Pat. No.6,607,977), which claims benefit of prior U.S. Provisional ApplicationNo. 60/275,803 filed Mar. 13, 2001. U.S. Pat. No. 6,764,940 also claimsbenefit of U.S. Provisional Patent Application No. 60/379,874 filed May10, 2002. Each of these references is incorporated herein by referencein its entirety for all purposes.

FIELD OF THE INVENTION

The present invention pertains to methods for forming a metal diffusionbarrier on an integrated circuit. More specifically, the methods includeat least two operations. The first operation deposits barrier materialvia PVD or CVD to provide some coverage. The second operation depositsan additional barrier material and simultaneously etches a portion ofthe barrier material deposited in the first operation.

BACKGROUND OF THE INVENTION

Integrated circuit (IC) manufacturers have traditionally used aluminumand aluminum alloys, among other metals, as the conductive metal forintegrated circuits. While copper has a greater conductivity thanaluminum, it has not been used because of certain challenges itpresents, including the fact that it readily diffuses into silicon oxideand degrades insulating electrical properties even at very lowconcentrations. Recently, however, IC manufacturers have been turning tocopper because of its high conductivity and electromigration resistance,among other desirable properties. Most notable among the IC metalizationprocesses that use copper is Damascene processing. Damascene processingis often a preferred method because it requires fewer processing stepsthan other methods and offers a higher yield. It is also particularlywell-suited to metals such as Cu that cannot readily be patterned byplasma etching.

Damascene processing is a method for forming metal lines on integratedcircuits. It involves formation of inlaid metal lines in trenches andvias formed in a dielectric layer (inter-metal dielectric). Damasceneprocessing is often a preferred method because it requires fewerprocessing steps than other methods and offers a higher yield. It isalso particularly well-suited to metals such as Cu that cannot readilybe patterned by plasma etching. In order to frame the context of thisinvention, a brief description of a copper dual Damascene process forforming a partially fabricated integrated circuit is described below.

Presented in FIGS. 1A-1G, is a cross sectional depiction of a dualDamascene fabrication process. Referring to FIG. 1A, an example of atypical substrate, 100, used for dual damascene fabrication isillustrated. Substrate 100 includes a pre-formed dielectric layer 103(such as silicon dioxide or organic-containing low-k materials) withetched line paths (trenches and vias) in which; a diffusion barrier 105has been deposited followed by inlaying with copper conductive routes107. Because copper or other mobile conductive material provides theconductive paths of the semiconductor wafer, the underlying silicondevices must be protected from metal ions (e.g., copper) that mightotherwise diffuse into the silicon. Suitable materials for diffusionbarrier 105 include tantalum, tantalum nitride, tungsten, titanium,titanium tungsten, titanium nitride, and the like. In a typical process,barrier 105 is formed by a physical vapor deposition (PVD) process suchas sputtering or a chemical vapor deposition (CVD) process. Typicalmetals for the conductive routes are aluminum and copper. Morefrequently, copper serves as the metal in damascene processes, asdepicted in these figures. The resultant partially fabricated integratedcircuit 101 is a representative substrate for subsequent Damasceneprocessing, as depicted in FIGS. 1B-1G.

As depicted in FIG. 1B, a silicon nitride or silicon carbide diffusionbarrier 109 is deposited to encapsulate conductive routes 107. Next, afirst dielectric layer, 111, of a dual damascene dielectric structure isdeposited on diffusion barrier 109. This is followed by deposition of anetch-stop layer 113 (typically composed of silicon nitride or siliconcarbide) on the first dielectric layer 111.

The process follows, as depicted in FIG. 1C, where a second dielectriclayer 115 of the dual damascene dielectric structure is deposited in asimilar manner to the first dielectric layer 111, onto etch-stop layer113. Deposition of an antireflective layer 117, typically a siliconoxynitride, follows.

The dual Damascene process continues, as depicted in FIGS. 1D-1E, withetching of vias and trenches in the first and second dielectric layers.First, vias 119 are etched through antireflective layer 117 and thesecond dielectric layer 115. Standard lithography techniques are used toetch a pattern of these vias. The etching of vias 119 is controlled suchthat etch-stop layer 113 is not penetrated. As depicted in FIG. 1E, in asubsequent lithography process, antireflective layer 117 is removed andtrenches 121 are etched in the second dielectric layer 115; vias 119 arepropagated through etch-stop layer 113, first dielectric layer 111, anddiffusion barrier 109.

Next, as depicted in FIG. 1F, these newly formed vias and trenches are,as described above, coated with a conformal diffusion barrier 123. Asmentioned above, barrier 123 is made of tantalum, titanium, or othermaterials that effectively block diffusion of copper atoms into thedielectric layers.

After diffusion barrier 123 is deposited, a seed layer of copper isapplied (typically a PVD process) to enable subsequent electrofilling ofthe features with copper inlay. FIG. 1G shows the completed dualDamascene process, in which copper conductive routes 125 are inlayed(seed layer not depicted) into the via and trench surfaces over barrier123.

Copper routes 125 and 107 are now in electrical contact and formconductive pathways, as they are separated by only by diffusion barrier123 which is itself somewhat conductive. Although conformal barrierlayers are sufficiently conductive for conventional circuitry, with thecontinuing need for faster (signal propagation speed) and more reliablemicrochip circuitry, the resistance of conformal barrier layers made ofthe materials mentioned above is problematic. The resistance of suchbarrier layers can be from ten to one hundred times that of copper.Thus, to reduce resistance between the copper routes, a portion of thediffusion barrier may be etched away, specifically at the via bottom, inorder to expose the lower copper plug. In this way, the subsequentcopper inlay can be deposited directly onto the lower copper plug.Conventional methods for etching away diffusion barriers at the bottomof vias (for example, the region of barrier 123 contacting copper inlay107 in FIG. 1F) are problematic in that they are not selective enough.That is, conventional etch methods remove barrier material fromundesired areas as well, such as the corners (edges) of the via, trench,and field regions. This can destroy critical dimensions of the via andtrench surfaces (faceting of the corners) and unnecessarily exposes thedielectric to plasma.

In addition, conventional etching methods do not address unlandedcontact regions. As illustrated in FIG. 1F, a portion of diffusionbarrier 123 located at via bottom 127 does not fully contact copperinlay 107. In this case, a portion of the barrier rests on copper inlay107 and a portion rests on dielectric 103. A conventional barrier etch,meant to expose copper inlay 107, would expose both copper inlay 107 anddielectric 103 in region 127. In that case, more process steps would beneeded to repair or replace diffusion barrier on the newly-exposedregion of dielectric 103, before any subsequent copper could bedeposited thereon. Using conventional unselective “blanket” conformaldeposition methods to re-protect the dielectric, one would create thesame problem that existed before the etch, that is, higher resistancebetween copper routes due to the barrier itself.

What is therefore needed are improved methods of forming diffusionbarriers on integrated circuit structures, selective methods in whichthe portion of the diffusion barrier at the bottom of vias is eithercompletely or partially removed without sacrificing the integrity of thediffusion barrier in other regions. In this way, the resistance betweeninlayed metal conductive routes is reduced.

SUMMARY OF THE INVENTION

The present invention pertains to methods for forming a metal diffusionbarrier on an integrated circuit in which the formation includes atleast two operations. The first operation deposits barrier material viaPVD or CVD to provide some minimal coverage. The second operationdeposits an additional barrier material and simultaneously etches aportion of the barrier material deposited in the first operation. Atleast part of the first operation is performed in the same reactionchamber as the second operation. Some preferred methods of the inventionare entirely done in a single process tool, without breaking vacuum. Theresult of the operations is a metal diffusion barrier formed in part bynet etching in certain areas, in particular the bottom of vias, and anet deposition in other areas, in particular the side walls of vias.Controlled etching is used to selectively remove barrier material fromthe bottom of vias, either completely or partially, thus reducing theresistance of subsequently formed metal interconnects. In some aspectsof the invention, selective etching is also used to remove contaminantsunder the barrier material, thus obviating a separate precleanoperation.

The invention accomplishes simultaneous etch and deposition by creationof unique plasma producing process conditions such that barrier materialis etched away in some regions while in other regions barrier materialis deposited. Thus, the descriptive term “etch to deposition ratio” or“E/D” is used from herein. More specifically, in the context of apartially fabricated integrated circuit having via and trench surfacefeatures, methods described herein provide that E/D varies as a functionof the elevation profile of the surface features to which the plasma isapplied. Generally, E/D is greatest at the bottom most regions of thewafer surface features and decreases in magnitude as elevationincreases.

In this invention, there are three E/D scenarios created by control ofprocess conditions. In the first scenario, E/D is greater than 1 at thevia bottom, on the trench step, and on the field region. In the secondscenario, E/D is greater than 1 at the via bottom and on the trenchstep, but less than one on the field region. In the third scenario, E/Dis greater than 1 at the via bottom, but less than 1 on the trench stepand on the field region. By using these three E/D scenarios, a varietyof stack barrier layer structures are realized.

A preferred material for this etch/deposition sputter is tantalum,although the invention is not limited to tantalum. Other materials forwhich the invention is applicable include but are not limited totitanium, tungsten, cobalt, solid solutions (interstitial forms) oftantalum and nitrogen, and binary nitrides (e.g. TaN_(x), TiN, WN_(x)).After diffusion barriers of the invention are formed, a metal conductivelayer is deposited thereon. Where methods of the invention create adiffusion barrier having no barrier material at the bottom of the vias,the metal conductive layer makes direct contact with exposed metalconductive routes. Thus, one aspect of the invention is a method fordepositing a diffusion barrier and a metal conductive layer for metalinterconnects on a wafer substrate. Such methods may be characterized bythe following sequence: (a) depositing a first portion of the diffusionbarrier over the surface of the wafer substrate, (b) etching through thefirst portion of the diffusion barrier at the bottom of a plurality ofvias while depositing a second portion of the diffusion barrierelsewhere on the wafer substrate, and (c) depositing the metalconductive layer over the surface of the wafer substrate such that themetal conductive layer contacts an underlying metal layer only at thebottom of the plurality of vias. Preferably at least part of (a) and allof (b) are performed in the same processing chamber. Additionally, thewafer may be precleaned before (a) in some preferred methods. In somepreferred embodiments, all of (a)-(c) are performed in the sameprocessing tool.

For unlanded vias (and in some instances for fully landed vias as well),methods of the invention create a diffusion barrier having minimalbarrier material at the bottom of the vias. In this case, the resistanceof the barrier between the metal conductive layer and underlying metalconductive routes is minimized. Thus, another aspect of the invention isa method for depositing a diffusion barrier and a metal conductive layerfor metal interconnects on a wafer substrate. Such methods may becharacterized by the following sequence: (a) precleaning the wafersubstrate, (b) depositing a first portion of the diffusion barrier overthe surface of the wafer substrate, (c) etching part-way through thefirst portion of the diffusion barrier at the bottom of a plurality ofvias while depositing a second portion of the diffusion barrierelsewhere on the wafer substrate such that the diffusion barrier has aminimum thickness at the bottom of the plurality of vias, and (d)depositing the metal conductive layer over the surface of the wafersubstrate. Preferably at least part of (b) and all of (c) are performedin the same processing chamber. In some preferred embodiments, all of(a)-(d) are performed in the same processing tool.

Preferably methods of the invention are used in Damascene processing inwhich the metal conductive layer and interconnects are made of copper.In some preferred methods of the invention, the metal conductive layeris a copper seed layer. Preferably seed layers of the invention areformed using PVD, but the invention is not limited in this way. Asmentioned, in some methods of the invention, all aspects of a processflow for forming a diffusion barrier and depositing a metal conductiveroute thereon are done in the same processing tool.

Methods of the invention create diffusion barriers having stackstructures. Distinct portions of each stack may be deposited (layered)using PVD, CVD, or other methods. Thus diffusion barriers of theinvention may have bilayered or trilayered structures. Preferably, theportions include at least one of tantalum, nitrogen-doped tantalum,tantalum nitride, and titanium silicon nitride. More detail of preferredarrangements for the layering of these materials, methods of depositing,and structure of the diffusion barriers formed therefrom, will bedescribed in the detailed description below.

Methods of the invention create diffusion barriers within integratedcircuitry using at least the materials described above. Therefore,another aspect of the invention pertains to an integrated circuit or apartially fabricated integrated circuit. Preferably integrated circuitsor partially fabricated integrated circuits of the invention include: adiffusion barrier which covers all surfaces of a plurality of vias and aplurality of trenches except that there is no diffusion barrier materialat the bottom of the plurality of vias, and a metal conductive layerprovided thereon, such that the metal conductive layer comes in directcontact with a plurality of metal conductive routes at the bottom of theplurality of vias. Particularly (but not necessarily) for unlanded vias,yet another aspect of the invention is an integrated circuit or apartially fabricated integrated circuit comprising: a diffusion barrierwhich covers all surfaces of a plurality of vias and a plurality oftrenches, said diffusion barrier having a thickness of between about 50and 400 Å on said surfaces except at the bottom of the plurality of viaswhere there is less than about 50 Å of diffusion barrier material; and ametal conductive layer provided thereon.

These and other features and advantages of the present invention will bedescribed in more detail below with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-G show cross sectional depictions of a copper dual Damascenefabrication process.

FIG. 2A presents aspects of a method for forming a diffusion barrier ofthe invention.

FIGS. 2B-E are cross-sectional depictions that illustrate variousaspects of a process flow for forming a diffusion barrier of theinvention as described in FIG. 2A.

FIG. 2F is a cross-sectional depiction of a portion of a partiallyfabricated integrated circuit of the invention that is made using aprocess flow similar to that described for FIGS. 2B-E.

FIG. 2G is a cross-sectional depiction of a portion of another partiallyfabricated integrated circuit of the invention that is made using aprocess flow similar to that described for FIGS. 2B-E.

FIG. 3A presents aspects of a method for forming another diffusionbarrier of the invention.

FIGS. 3B-E are cross-sectional depictions that illustrate variousaspects of a process flow for forming another diffusion barrier of theinvention as described in FIG. 3A.

FIG. 3F is a cross-sectional depiction of a portion of a partiallyfabricated integrated circuit of the invention that is made using aprocess flow similar to that described for FIGS. 3B-E.

FIG. 3G is a cross-sectional depiction of a portion of another partiallyfabricated integrated circuit of the invention that is made using aprocess flow similar to that described for FIGS. 3B-E.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description of the present invention, numerousspecific embodiments are set forth in order to provide a thoroughunderstanding of the invention. However, as will be apparent to thoseskilled in the art, the present invention may be practiced without thesespecific details or by using alternate elements or processes. In otherinstances well-known processes, procedures and components have not beendescribed in detail so as not to unnecessarily obscure aspects of thepresent invention.

In this application, the term wafer will be used interchangeably withpartially fabricated integrated circuit. One skilled in the art wouldunderstand that the term “partially fabricated integrated circuit” canrefer to a silicon wafer during any of many stages of integrated circuitfabrication thereon. Thus, “wafer”, “wafer substrate”, and “substrate”are all used interchangeably.

As mentioned, the invention finds particular use in Damasceneprocessing. FIGS. 2A and 3A present aspects of process flows for formingdiffusion barriers of the invention. Typically, the process flows areperformed in the context of copper Damascene processing. One can referback to FIGS. 1A-1G for a slightly broader context. Specifically,referring to FIG. 1E, once vias and trenches have been formed in awafer, typically a diffusion barrier will be formed thereon. For wafersubstrates having vias that are entirely landed over underlying metalsurfaces, methods of the invention which etch through barrier materialat the bottom of vias are preferable. In some instances a wafersubstrate may have unlanded vias (as described in the background sectionin reference to FIG. 1E). For wafer substrates having unlanded vias,methods of the invention that etch the barrier material at the bottom ofthe vias to a minimum are preferred.

Also as mentioned, the invention accomplishes simultaneous etch anddeposition by creation of unique plasma producing process conditionssuch that barrier material is etched away in some regions while in otherregions barrier material is deposited. More specifically, methodsdescribed herein provide that E/D varies as a function of the elevationprofile of the surface features to which the plasma is applied.Generally, E/D is greatest at the bottom most regions of the wafersurface features and decreases in magnitude as elevation increases. Inthis invention, there are three E/D scenarios created by control ofprocess conditions. In the first scenario, E/D is greater than 1 at thevia bottom, on the trench step, and on the field region. In this firstscenario, deposition of barrier material (occurring simultaneously withetch) occurs only on the side walls of the wafer surface features. Inthe second scenario, E/D is greater than 1 at the via bottom and on thetrench step, but less than one on the field region. In this secondscenario, deposition of barrier material (occurring simultaneously withetch) occurs not only on the side walls of the wafer surface features,but also on the field. In the third scenario, E/D is greater than 1 atthe via bottom, but less than 1 on the trench step and on the fieldregion. In this third scenario, deposition of barrier material(occurring simultaneously with etch at the via bottom) occurs not onlyon the side walls but also on the trench and field.

A method 200, of forming diffusion barriers of the invention will now bedescribed with reference to the flow chart of FIG. 2A and associatedschematic diagrams in FIGS. 2B-2E. Note that in many embodiments, eachof the depicted process operations are carried out using processconditions and materials specific to a particular desired outcome.Specific examples will be discussed in detail below.

Referring to FIG. 2A, aspects of a process flow, 200, for forming adiffusion barrier of the invention are depicted. A first portion of thediffusion barrier is deposited over the surface of the wafer. See 201.

Referring to FIG. 2B, a typical substrate, 202, is illustrated.Substrate 202 includes a pre-formed dielectric layer 207 (such assilicon dioxide or organic-containing low-k materials) with etched linepaths (trenches and vias) in which; a diffusion barrier 209 has beendeposited followed by inlaying with copper conductive route 211. Asilicon nitride or silicon carbide barrier layer 213 was laid thereon,followed by another layer of dielectric material, 215. After processsteps (including lithography) for example as outlined in the backgroundsection above, dielectric layer 215 has etched trench 219 and via 221.Note that included in this surface feature are horizontal surfaces(field 217, step 220 of trench 219, and bottom of via 221) and verticalsurfaces (the side walls of the via and trench). At the bottom of via221, copper conductive route 211 is exposed. In some embodiments it isdesired to preclean contaminants from these features before depositionof barrier material, this can be done in the same processing chamber ornot. In other embodiments, the simultaneous etch/deposition (asdescribed below) is used to remove surface contaminants from the viabottom by etching through a barrier material thereon. In this way, thebarrier is removed only at the via bottom and the exposed copper iseffectively cleaned (etched) by exposure to the plasma. Contaminantsinclude residues left from etch and photoresist clean processes andoxides of copper in some instances.

Again referring to 201 in FIG. 2A, deposition of the first portion ofthe diffusion barrier may be done using PVD or CVD. Preferably, thefirst portion of the diffusion barrier includes at least one oftantalum, nitrogen-doped tantalum, tantalum nitride, and titaniumsilicon nitride. Tantalum, nitrogen-doped tantalum, and tantalum nitrideare preferably deposited using PVD. As mentioned, other materials forwhich the invention is applicable include but are not limited totitanium, tungsten, cobalt, solid solutions (interstitial forms) oftantalum and nitrogen, and binary nitrides (e.g. TaN_(x), TiN, WN_(x)).These materials would also preferably be deposited by PVD. Titaniumsilicon nitride is preferably deposited using CVD. The first portion ofthe diffusion barrier is preferably a conformal (contour following,continuous, and of relatively uniform thickness) monolayer. In thisdescription, the term “monolayer” is meant to mean a single layer ofmaterial, not necessarily a single atomic or molecular layer as the termis sometimes used. In some embodiments, a bilayer is preferred for thefirst portion of the diffusion barrier.

FIG. 2C depicts substrate 202, after deposition of the first portion ofthe diffusion barrier. In this example the first portion is a conformalmonolayer 223 that covers all surfaces of substrate 202. Preferably, themonolayer is between about 50 and 300 Å thick on the field of the wafer,more preferably about 100 Å thick.

Referring to FIG. 2A, once the first portion of the diffusion barrier isdeposited, simultaneous etch/deposition is used to etch through thefirst portion of the diffusion barrier at the bottom of the vias whiledepositing a second portion of the diffusion barrier elsewhere on thewafer. See 203. Preferably the second portion of the diffusion barrieris a sputtered metal. Even more preferably, the sputtered metal istantalum. FIG. 2D depicts substrate 202 after such an etch/depositionprocess in which the etch to deposition ratio was greater than 1, bothin the bottom of via 221 and on the horizontal surfaces (field 217 andstep 220 (see FIG. 2B)). The relative rate of etch was controlled suchthat step 220 and field 217 were minimally etched relative to the bottomof via 221. Thus, the first portion 223 is etched through at the bottomof via 221, exposing the surface of copper conductive route 211. See225. Concurrent with the etch, barrier material 227 (the second portion)is deposited on the side walls of the via and trench. Preferably, thesecond portion will have between about 25 and 100 Å of barrier material.Additionally, there is minimal faceting of the corners (unlikeconventional etching methods). See 229.

Thus, the resulting structure 202 has a diffusion barrier (bilayer) thatincludes first portion 223 and second portion 227. The diffusion barrieris discontinuous, in that it does not cover copper conductive route 211.Note that even though plasma etch was used and copper route 211 wasexposed, the dielectric layers were not exposed to plasma during themethod. This is a distinct advantage over conventional diffusion barrierformation methods which involve a plasma etch.

Note also that in some instances it has been experimentally determinedthat there may be a finite amount of the barrier material (e.g.tantalum) implanted into the copper conductive route surface at thebottom of the via. In this invention, this scenario is still consideredto mean “exposed copper” at the via bottom, since the tantalum isimplanted into the copper and subsequent copper seed layer or inlaymakes direct contact with this “doped” copper surface.

Referring again to FIG. 2A, once the diffusion barrier is formed, ametal conductive layer 231 is deposited over the surface of the wafersuch that the metal conductive layer contacts the underlying metal layeronly at the bottom of the vias. See 205. FIG. 2E depicts substrate 202after deposition of metal conductive layer 231. In this example, themetal conductive layer is a copper seed layer, but the invention is notlimited to seed layers. For example, the metal conductive layer cancomprise an electroless metal fill. Once the metal conductive layer isdeposited, the method 200 is done.

As illustrated in FIG. 2E, newly deposited metal conductive layer 231now is in direct contact with underlying copper inlay 211. Substrate 202is now ready for bulk electrochemical or electroless fill for formationof conductive routes that will fill completely its surface features.

In the above description, and as illustrated in FIGS. 2D-E, the secondportion (227) of the barrier layer is deposited only on the side wallsof the surface features of substrate 202. Some methods of the inventionuse etch to deposition ratios greater than one at the via bottom, butless than one on the field and trench regions. In this case, the secondportion of barrier material will be deposited on the field and trench aswell as the side walls. Preferably, the second portion will have betweenabout 50 and 500 Å of barrier material deposited on the field andhorizontal trench surfaces. FIG. 2F, depicts the resulting structure 204obtained (after seed layer deposition). Structure 204 is similar tostructure 202 (depicted in FIG. 2E), except that a diffusion barrier isformed in which second portion 227 now covers all of the remaining firstportion 223 (that which was not etched through). Thus, E/D in the trenchand on the field was less than one, while at the bottom of the via, E/Dwas greater than one. Copper conductive route 211 was still exposed atthe bottom of the via (due to E/D>1) and thus seed layer 231 is indirect contact with 211, analogous to structure 202 (FIG. 2E).

In another preferred method of the invention, the first portion of thediffusion barrier will be a bilayer, and once the second portion isdeposited a trilayer will result. If the first portion of the diffusionbarrier is a bilayer, the bilayer will be made of a first depositedlayer and a second deposited layer thereon. Either of the first orsecond deposited layers of the bilayer may include at least one oftantalum, nitrogen-doped tantalum, tantalum nitride, and titaniumsilicon nitride. These materials are preferably deposited as mentionedabove. FIG. 2G depicts an example substrate 206, having such a trilayerdiffusion barrier. In this case, a conformal layer 223 is deposited overthe surface of the wafer, then another conformal layer 224 is depositedthereon (co-continuous, covering the entire surface). Once the bilayer(first portion) is deposited, then the second portion of the diffusionbarrier is deposited using the simultaneous etch/deposition method. Inthis example, the second portion, 227, is deposited only on the sidewalls and layers 223 and 224 are etched though at the bottom of the via.The resulting barrier layer is the trilayer structure depicted in FIG.2G (shown with copper seed layer 231 deposited on the diffusionbarrier). Alternatively, second portion 227 can be deposited on thetrench and field horizontal surfaces as well as the side walls.

Diffusion barrier stack structures (bilayers, trilayers, etc.) canprovide better protection against metal diffusion than single layers dueto the combined properties of the individual layers of which they aremade. In some cases, multi-layered diffusion barriers can also be madethicker to serve as a fill element. For example, in some low-kdielectric applications, lithography leaves the dielectric withundercuts (notches) or bowing (concavity) in the side walls. Thesedefects can be repaired by deposition of extra barrier material whichfills the defects. Judicious combinations of CVD and PVD methods areused to achieve this end. One problem with this approach is theresistance at the via bottom due to multiple layers of barrier material.The instant invention solves this problem. For example, depending on theneed, in accordance with FIG. 2G, layer 223 or layer 224 may bedeposited using either CVD or PVD. Methods of the invention enhancedefect repair methodology by providing methods that either remove orminimize unwanted barrier material at the bottom of the vias.

In order to describe formation of diffusion barriers intended primarily(but not necessarily) for unlanded vias, a method 300, of formingdiffusion barriers of the invention will now be described with referenceto the flow chart of FIG. 3A and associated schematic diagrams in FIGS.3B-3E. Again, note that in many embodiments, each of the depictedprocess operations are carried out using process conditions andmaterials specific to a particular desired outcome. The invention is notlimited to these specific embodiments, but rather they are intended toillustrate the invention.

Referring to FIG. 3A, aspects of a process flow, 300, for forming adiffusion barrier of the invention are depicted. The wafer isprecleaned. See 301. Precleaning is performed in the case of unlandedvias, because subsequently deposited barrier material will not be fullyetched through at the bottom of the via. Thus any contaminants thatreside on the via prior to deposition of barrier material would remainthere if not removed in a preclean operation. Next, a first portion ofthe diffusion barrier is deposited over the surface of the wafer. See303.

Referring to FIG. 3B, a typical substrate, 302, is illustrated.Substrate 302 includes a pre-formed dielectric layer 309 (such assilicon dioxide or organic-containing low-k materials) with etched linepaths (trenches and vias) in which; a diffusion barrier 311 has beendeposited followed by inlaying with copper conductive route 313. Asilicon nitride or silicon carbide barrier layer 315 was laid thereon,followed by another layer of dielectric material, 317. After processsteps (including lithography) for example as outlined in the backgroundsection above, dielectric layer 317 has etched trench 321 and via 323.Note that included in this surface feature are horizontal surfaces(field 319, step 322 of trench 321, and the bottom of via 323) andvertical surfaces (the side walls of the via and trench). The surfacearea at the bottom of via 323, includes a portion of exposed copperconductive route 313 and a portion of exposed dielectric 309. Asmentioned, it is desired to preclean (preferably in the same processingtool) contaminants from these surfaces prior to deposition of barriermaterial. Contaminants include residues left from etch and photoresistclean processes and oxides of copper in some instances.

Again referring to 303 in FIG. 3A, deposition of the first portion ofthe diffusion barrier may be done using PVD or CVD. Preferably, thefirst portion of the diffusion barrier includes at least one oftantalum, nitrogen-doped tantalum, tantalum nitride, and titaniumsilicon nitride. Tantalum, nitrogen-doped tantalum, and tantalum nitrideare preferable deposited using PVD. Titanium silicon nitride ispreferably deposited using CVD. The first portion of the diffusionbarrier is preferably a conformal monolayer. In some embodiments, abilayer is preferred for the first portion of the diffusion barrier.FIG. 3C depicts substrate 302, after deposition of the first portion ofthe diffusion barrier. In this example the first portion is a conformalmonolayer 325 that covers all surfaces of substrate 302. Preferably, themonolayer is between about 50 and 300 Å thick on the field of the wafer,more preferably about 100 Å thick.

Referring to FIG. 3A, once the first portion of the diffusion barrier isdeposited, simultaneous etch/deposition is used to etch part way throughthe first portion of the diffusion barrier at the bottom of the viaswhile depositing a second portion of the diffusion barrier elsewhere onthe wafer. Preferably, this process creates a diffusion barrier having aminimum thickness at the bottom of the via. See 305. Preferably, theminimum thickness will be between about 30 and 1001 while the diffusionbarrier on the side walls and horizontal surfaces is between about 50and 400 Å thick.

FIG. 3D depicts substrate 302 after such an etch/deposition process inwhich the etch to deposition ratio was greater than 1, both in thebottom of via 323 and on the horizontal surfaces (field 319 and step 322(see FIG. 3B)). The relative rate of etch was controlled such that step322 and field 319 were minimally etched relative to the bottom of via323. Thus, the first portion 325 is etched to a minimum thickness at thebottom of via 323. See 327. Barrier material 329 (the second portion) ishowever deposited on the side walls of the via and trench. Preferably,the second portion will have between about 25 and 100 Å of barriermaterial. Additionally, there is minimal faceting of the corners (unlikeconventional etching methods). See 331. Thus, the resulting structure302 has a diffusion barrier (bilayer) that includes continuous firstportion 325 and discontinuous second portion 329.

Referring again to FIG. 3A, once the diffusion barrier is formed, ametal conductive layer 333 is deposited over the surface of the wafersuch that the metal conductive layer contacts the underlying metal layeronly at the bottom of the vias. See 307. FIG. 3E depicts substrate 302after deposition of metal conductive layer 333. In this example, themetal conductive layer is a copper seed layer, but the invention is notlimited to seed layers. Once the metal conductive layer is deposited,the method 300 is done.

As illustrated in FIG. 3E, newly deposited metal conductive layer 333 isseparated from underlying copper inlay 313 by a region of the diffusionbarrier having minimal thickness. Preferably between about 25 and 300 Åare removed to provide this minimal thickness. Substrate 302 is nowready for bulk electrofill (or electroless metal deposition) forformation of conductive routes which will fill completely its surfacefeatures.

In the above description, and as illustrated in FIGS. 3D-E, the secondportion of the barrier layer is deposited only on the side walls of thesurface features of substrate 302. As mentioned, some methods of theinvention use etch to deposition ratios greater than one at the viabottom, but less than one on the field and trench regions. In this case,the second portion of barrier material will be deposited on the fieldand trench as well as the side walls. Preferably, the second portion hasbetween about 50 and 500 Å of barrier material deposited on the fieldand horizontal trench surfaces.

FIG. 3F, depicts the resulting structure 304 obtained (after seed layerdeposition) using such an E/D scenario. Structure 304 is similar tostructure 302 (depicted in FIG. 3E), except that a diffusion barrier isformed in which first portion 325 is continuous over the surface of thewafer and second portion 329 covers all of first portion 325 except atthe bottom of the via. As second portion 329 was deposited, firstportion 325 was partially etched at the via bottom. Thus, E/D in thetrench and on the field was less than one, while at the bottom of thevia, E/D was greater than one.

In another preferred method of the invention, the first portion of thediffusion barrier will be a bilayer, and once the second portion isdeposited a trilayer will result. As in the methods for fully landedvias, if the first portion of the diffusion barrier is a bilayer, thebilayer will have a first deposited layer and a second deposited layerthereon. Either of the first or second deposited layers of the bilayermay include at least one of tantalum, nitrogen-doped tantalum, tantalumnitride, and titanium silicon nitride. These materials are preferablydeposited as mentioned above.

FIG. 3G depicts an example substrate 306, having such a trilayerdiffusion barrier. In this case, a conformal layer 325 is deposited overthe surface of the wafer, then another conformal layer 326 is depositedthereon. Once the bilayer (first portion) is deposited, then the secondportion of the diffusion barrier is deposited using the simultaneousetch/deposition method. In this example, the second portion, 329, isdeposited only on the side walls. At the same time, layer 326 ispreferably etched through and layer 325 is etched only part way throughat the bottom of the via. The resulting barrier layer is the trilayerstructure depicted in FIG. 3G.

Alternatively, only layer 326 is etched wholly or partially, leavinglayer 325 intact, resulting in a diffusion barrier having a minimumthickness at the bottom of the via. Also, alternatively, second portion329 can be deposited on the trench and field horizontal surfaces as wellas on the side walls.

Experimental

As mentioned, methods of the invention employ a simultaneousetch/deposition to etch barrier material at the via bottom whiledepositing barrier material elsewhere on a wafer substrate. As well,various aspects of process flows involve deposition of barrier materials(either by CVD or PVD), precleaning, and degassing operations. Incertain preferred embodiments all these process steps are done in thesame processing tool. One tool that allows degas, preclean, CVDdeposition, and PVD deposition all under the same vacuum is the NOVATool available from Novellus Systems of San Jose, Calif. Therefore, oncea wafer is in the tool and a vacuum is established, at least in someembodiments, all of the above described process aspects are performedwithout breaking vacuum. Only sources are changed during the operation,e.g. changing from a CVD source to a PVD source. For example, a wafer isplaced into the apparatus, it is degassed, precleaned (for example withan argon plasma), a first deposited layer of barrier material is appliedvia CVD (e.g. titanium silicon nitride), a second deposited layer isapplied via PVD (e.g. tantalum nitride). The first and second depositedlayers make the first portion of the diffusion barrier. Finally, atantalum etch/deposition process is carried out which deposits thesecond portion of the diffusion barrier and etches at least the bottomof the via, forming the final diffusion barrier structure.

Preferably the simultaneous etch/deposition is carried out usinghollow-cathode magnetron (HCM) sputtering. Such devices are described inU.S. Pat. No. 5,482,611, naming Helmer et al. as inventors, U.S. Pat.Nos. 6,179,973 B1 and 6,193,854 B1, naming Lai et al. as inventors, andU.S. Pat. No. 6,217,716 B1 naming Fai Lai as the inventor. If thebarrier material to be deposited is tantalum, a tantalum target sourceis used.

Preferable process conditions for include a pressure of between about0.1 and 100 mTorr. Argon flows are between about 50 and 300 SCCM(standard cubic centimeters per minute). When E/D>1 is desired both atthe bottom of the vias and in the field, a DC source power of betweenabout 1 and 10 kW (low power embodiments) is applied to the tantalumtarget. When an E/D>1 is desired at the bottom of the vias, but E/D<1 inthe field is desired, a DC source power of between about 10 and 30 kW(high power embodiments) is applied to the tantalum target. The m-coil(electromagnetic coil for controlling field shape and thus plasma flux)current used is between about 0.1-2.0 A, preferably about 1 A. The wafertemperature is manipulated using a temperature controlled stage, thewafer temperatures used are between about −100 and 100° C., preferablyabout −50° C. The wafer is biased with an RF frequency source (locatedbelow or in proximity to the stage). For methods where it is intended toetch through vias, the RF frequency is preferably between about 100 kHzand 50 MHz. For methods where it is intended to etch only part waythrough vias, the RF frequency is preferably between about 100 kHz and50 MHz. The RF power applied is preferably between about 100 and 500 W.In preferred embodiments, the amount of sputtering is controlled by theRF power at fixed RF frequency. Various RF frequencies can be used toachieve this effect. One preferred RF frequency is 13.56 MHz.

In general, etch rate is most strongly related to the RF power, whilethe deposition rate is most strongly related to the DC source power. TheE/D ratio depends predominantly on the ratio of RF power (table) to DCpower (source). The higher the RF/DC power ratio, the higher the E/Dratio on the wafer. The etch rate is largely dependent on RF power andpressure since these parameters control the energy of Ar ions near thewafer. The deposition rate is largely dependent on DC power since thisparameter affects the flux and energy of Ar ions near the surfacetarget.

While not wishing to be bound by theory, it is believed that the RFfrequency creates anisotropic plasma conditions. The etch/depositionratio (E/D) can be controlled so that it is >1 in the via bottom and(resulting in a net etching), and >1 or <1 on the trench and fieldhorizontal surfaces. The magnitude of E/D on the side walls is <1because the plasma flux is directed primarily toward the wafer surface(parallel with the side walls). Thus, only horizontal surfaces (withrelatively large surface areas (compared to the side walls)) areeffectively etched by the impinging plasma flux. The side walls receivea net deposition.

If tantalum nitride or nitrogen-doped tantalum is the barrier materialto be deposited, a nitrogen source such as N₂ will be used at 10-100SCCM, preferably about 30 SCCM in conjunction with argon. Titaniumsilicon nitride is deposited by CVD using a technique described in U.S.patent application Ser. No. 09/965,471, entitled “Method of Depositing aDiffusion Barrier for Copper Interconnection Applications” filed bySuwwan de Felipe on the same date as this application, or U.S. patentapplication Ser. No. 09/862,539, titled “Improved Deposition ofConformal Copper Seed Layers by Control of Barrier Layer Morphology”filed by Suwwan de Felipe on May 21, 2001.

As mentioned, methods of the invention form diffusion barriers havingstacked structures. Both methods primarily intended for fully landedvias (etch through at via bottom) and methods primarily intended forunlanded vias (partial etch at via bottom) form bilayered and trilayereddiffusion barriers. Illustrative structures of diffusion barriers of theinvention were described above with reference to the figures. The tablebelow summarizes further aspects of some preferred embodiments of theinvention. Each of the twelve listed diffusion barriers may varyaccording to the particular thickness of the deposited layers, andwhether or not material is deposited only on the side walls or on theside walls and the field and horizontal trench regions during thesimultaneous etch deposition (E/D) process step. Therefore this table ismeant to emphasize some preferred stack compositions as well asparticular methods used to form them. The symbol “Ta(N)” is meant todesignate tantalum with some nitrogen content. This can benitrogen-doped tantalum, solid solutions (interstitial forms) oftantalum and nitrogen, or tantalum nitrides. Titanium silicon nitride isdesignated by “TiN(Si).”

TABLE Preferred Diffusion Barriers of the Invention. Diffusion Pre-Barrier Barrier Barrier Barrier clean Material 1 Material 2 Material 3 1 no HCM Ta(N) Ta E/D etch through —  2 no CVD TiN(Si) Ta E/D etchthrough —  3 yes HCM Ta(N) Ta E/D etch partial —  4 yes HCM Ta(N) Ta E/Detch through —  5 no HCM Ta(N) CVD TiN(Si) Ta E/D etch through  6 yesHCM Ta(N) CVD TiN(Si) Ta E/D etch partial  7 yes HCM Ta(N) CVD TiN(Si)Ta E/D etch through  8 no CVD TiN(Si) HCM Ta(N) Ta E/D etch through  9yes CVD TiN(Si) HCM Ta(N) Ta E/D etch partial 10 yes CVD TiN(Si) HCMTa(N) Ta E/D etch through 11 yes CVD TiN(Si) Ta E/D etch through — 12yes CVD TiN(Si) Ta E/D etch partial —

Although various details have been omitted for clarity's sake, variousdesign alternatives may be implemented. Therefore, the present examplesare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein, but may bemodified within the scope of the appended claims.

What is claimed is:
 1. A method for depositing a metal-containingmaterial on a substrate, the method comprising: (a) receiving a wafersubstrate comprising at least one via comprising a bottom portion, atleast one trench having a horizontal surface, and a field, wherein thesubstrate comprises an exposed metal at the bottom portion of the atleast one via; (b) depositing a first portion of the metal-containingmaterial at least over the bottom portion of the at least one via usinga metal from a deposition source; (c) etching away the first portion ofthe metal-containing material at the bottom of the at least one via,such that an E/D (etch rate to deposition rate) ratio is greater than 1at the bottom of the at least one via, with energetic inert gas ionswithout fully etching through to partially remove the first portion ofthe metal-containing material such that a part of the first portion ofthe metal-containing material remains at the bottom of the at least onevia and a part of the first portion of the metal-containing material isremoved from the bottom portion of the at least one via, such that theresistance of subsequently formed interconnects is reduced relative tothat of interconnects formed using the first portion of themetal-containing material prior to etching, while simultaneouslydepositing a second portion of the metal-containing material in thetrench and/or field on the wafer substrate, comprising a PVDetch/deposition process in which the wafer substrate is biased with anRF frequency source such that the etch rate at the bottom of the atleast one via is greater than an etch rate on any associated horizontaltrench surfaces or the field.
 2. The method of claim 1, wherein the RFfrequency is between about 100 kHz and 50 MHz.
 3. The method of claim 1,further comprising using a source power of between about 1 and 10 kW. 4.The method of claim 3, further comprising using an RF power of about 350W.
 5. The method of claim 4, further comprising using an Ar flow ofabout 10 to 300 SCCM.
 6. The method of claim 5, further comprising usinga pressure of 0.1-100 mTorr.
 7. The method of claim 5, furthercomprising using a pressure of about 8 mTorr.